How yarn thickness is determined: complete guide to the Nm count

In the world of yarns, one of the most frequent questions is:

“How thick is this yarn?”

The answer, however, is not as immediate as it seems. Unlike other materials, yarn thickness is not measured in millimeters, but through a technical system called yarn count, and one of the most widely used is Nm (Metric Number).

In this article, I will explain simply and professionally:

• what Nm means
• how yarn thickness is determined
• why two yarns with the same Nm can seem different

What is the Nm (Metric Number) count

The Nm (Metric Number) indicates how many meters of yarn there are in 1 gram of weight.

👉 Basic formula:
Nm = meters / grams

Example:

• Nm 1 = 1 meter weighs 1 gram → very thick yarn
• Nm 10 = 10 meters weigh 1 gram → finer yarn
• Nm 28 = 28 meters weigh 1 gram → very fine yarn

Fundamental rule:

👉 Higher Nm = finer yarn
👉 Lower Nm = thicker yarn

How yarn thickness is determined

The actual thickness of a yarn depends on 3 main factors:

The count (Nm) is the technical basis. It tells you how fine a single fiber is.

The number of plies (twisted strands)

You often see writings like:

• 2/28
• 2/13
• 3/15

What does it mean?

👉 The first number = number of twisted strands
👉 The second number = count of the single strand

Example:

• 2/28 = 2 strands of Nm 28 twisted together
• 2/13 = 2 strands of Nm 13 → much thicker

📌 More plies = fuller and thicker yarn

How it is worked (tension, stitch, machine)

Even with the same yarn:

• loose work = softer and bulkier
• tight work = more compact and thinner
• English rib vs stockinette = completely changes the volume

👉 So: perceived thickness ≠ only Nm

Why two yarns with the same Nm can be different

This is the most confusing part.

Two yarns, both Nm 2/28, can turn out to be:

• one fuller
• one more “hollow”
• one softer
• one stiffer

Depends on:

• fiber type (cashmere vs merino vs cotton)
• fiber length
• twist (more or less twisted)
• finishing process (washing, fulling, napping)

👉 Real example:
A recycled cashmere Nm 2/28 can appear more voluminous than a new cashmere with the same count.

Nm and practical use (needles and machines)

Here's a simple guide based on real experience:

• Nm 2/28
  • machine gauge 12 (1 ply)
  • needles: 2 plies → needles 3-4
• Nm 2/13
  • machine gauge 7-8
  • needles: 4-5
• Nm 1/3 – 1/5
  • very thick yarns
  • needles: 6-10

👉 But beware: these are always guidelines, not absolute rules.

Common mistake: thinking Nm = actual thickness

One of the most common mistakes is believing that Nm precisely defines thickness.

❌ Wrong
✔️ Nm defines the theoretical fineness of the thread, not the final result

👉 You only see the actual thickness by:

• working the swatch
• washing it
• observing the fiber's behavior

Professional advice

If you knit or produce knitwear:

👉 Never trust only the Nm

Always do:

1. a swatch
2. washing
3. final evaluation

This is even more true with:

• recycled cashmere
• untreated natural yarns
• yarn stock

The Nm system is a fundamental tool for understanding yarn, but it is not sufficient on its own.

To choose the right yarn, you must consider:

• count (Nm)
• number of plies
• fiber type
• processing

👉 Only then can you truly predict the final result.